this.Browser.DocumentTitleChanged += Browser_DocumentTitleChanged;
private void Browser_DocumentTitleChanged(object sender, EventArgs e)
{
Uri url = ((WebBrowser)sender).Document.Url;
txtUrl.Text = url.ToString();
}
или
this.Browser.Navigating += Browser_Navigating;
private void Browser_Navigating(object sender, WebBrowserNavigatingEventArgs e)
{
Uri url = e.Url;
txtUrl.Text = url.ToString();
}